1. Technical Field
This invention relates to windmills, and more particularly to a windmill vane having only a rigid planar support frame oriented forty-five degrees (45.degree.) relative to the instantaneous direction of movement of the vane, and a resilient sail mounted on the support frame.
An obstacle to modern use of wind power is the low cost-effectiveness of present windmill designs. Most simple, low-cost windmill designs convert too little of the available wind power into usable shaft power, while greater efficiencies have required more sophisticated and expensive designs. Windmills providing high power conversion efficiencies with simple designs using low-cost materials, have the potential of increasing the use of windmills as effective and reliable sources of energy.
The efficiency with which a windmill converts wind power into usable power depends primarily on the efficiency of the members which are acted upon by the wind. Windmills having a horizontal shaft and vertical vanes facing into the wind have existed since the latter part of the first millennium A.D., and were substantially perfected by the Dutch in the seventeenth century. The last two centuries have seen the birth and refinement of other windmill designs, in particular vertical shaft designs capable of extracting power from wind blowing in any direction. The efficiency of a vertical axis windmill depends primarily on the net efficiency of its vanes or sails. A windmill vane's net efficiency is defined as the difference between the power extracted from the wind when the vane is moving with the wind, less the drag produced when the vane is moving against the wind. Much inventive effort has been directed toward improving the net efficiency of vanes or sails for vertical axis windmills.
2. Description of the Prior Art
Graybill U.S. Pat. No. 3,995,170 shows a vertical axis windmill having vertical vanes with flexible sails 21, each sail being folded around a vertical post 17 when the vane is rotated against the wind. DeBerg U.S. Pat. No. 4,191,507 shows a vertical axis windmill having horizontal vanes with flexible sails, each sail being fastened along its upper edge to a radially extending sail arm, and being tethered by a plurality of cords 40 to a radially extending cord arm spaced horizontally from and lower than the sail arm, such that the sail is lifted into a substantially flat position to provide little resistance to the wind when the vane is moving against the wind. Both DeBerg and Graybill rely on a large number of moving parts subject to wear and eventual failure, thus reducing the operating reliability and the means time between failures of their designs.